import React, { Component } from 'react';

export default class Count extends Component {
    //按住alt键，可以选择多个
    state={count:0}
    increment=()=>{
      const {value}=this.selectNum;
      const {count}=this.state
      this.setState({count:count+value*1})
    }
    decrement=()=>{
        const {value}=this.selectNum;
        const {count}=this.state
        this.setState({count:count-value*1})
    }
    incrementIfOdd=()=>{
        const {value}=this.selectNum;
        const {count}=this.state
        console.log(count%2===0)
        if(count%2!==0){
            this.setState({count:count+value*1})
        }
       
    }
    incrementAsync=()=>{
        const {value}=this.selectNum;
        const {count}=this.state
        setTimeout(()=>{
            this.setState({count:count+value*1})
        },500)
            
        
    }
    render() {
        return (
            <div>
                <h1>当前求和:{this.state.count} </h1>
                <select ref={c=>{this.selectNum=c}}>
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3">3</option>
                </select>
               <button onClick={this.increment}>+</button>
               <button onClick={this.decrement}>-</button>
               <button onClick={this.incrementIfOdd}>当前求和为奇数再加</button>
               <button onClick={this.incrementAsync}>异步加</button>
            </div>
        );
    }
}
